1. Field of the Invention
The present invention relates to a wafer carrier, and in particular to a wafer carrier device capable of detecting the positioning precision of its supporting plate.
2. Description of the Related Art
At present, semiconductor wafers tend to have larger and larger sizes, wherein the manufacturing techniques for forming wafers have evolved from 6-inch wafers, to 12-inch wafers. The increase in wafer size also increases manufacturing costs for each wafer. Therefore, it is a priority to reduce the redundancy rate of wafers during manufacture as well as minimize pollution from improper processing of damaged wafers.
Wafers are damaged most frequently when processed in a wafer storage chamber or a reaction chamber and/or when conveyed to different locations by a carrier. Over time, the supporting plate and the automatic manipulator such as a mechanical arm that carry wafers tend to lose their positioning precision. As a result, the wafer cannot be accurately conveyed to predetermined positions, causing uneven temperature distribution or chemical deposition, erratic exposure, scratching, or even collision between wafers may occur, causing severe equipment damage.
Moreover, the defective wafers are typically not sorted out until most of the manufacturing process has been carried out. Namely, the operator of the process cannot be made aware before or during the mishap. As a result, the manufacturing cost is increased while the projected time of delivery is delayed. The above problem is further complicated since the exact cause of the problem cannot be pinpointed, which makes the situation even more difficult and therefore increases required repair time.
Therefore, precise positioning of the supporting plate on a carrier device is important to improve stability of the semiconductor manufacturing process.
Accordingly, an object of the present invention is to provide a wafer carrier device capable of detecting the positioning precision of its supporting plate, avoiding the above mentioned positioning problems.
In the wafer carrier device of the present invention, a supporting plate has three reflectors and a positioning window, and a mechanical arm connected to the supporting plate. A detection device has an alignment signal generator to output a first signal through the positioning window as an alignment signal, and three level detectors to each output a second signal to corresponding reflectors and receive a corresponding reflected level detection signal from the corresponding reflector. An alignment signal receiver receives the alignment signal, and a determining unit coupled to the alignment signal receiver and the detection device determines whether the supporting plate is aligned with the alignment signal receiver according to the alignment signal, and whether the supporting plate is in a horizontal orientation according to the three corresponding level detection signals. The determining unit outputs a position rectification signal when the supporting plate is aligned with the alignment signal receiver, and outputs a warning signal when horizontal orientation is not detected. A driver coupled to the determining unit moves the mechanical arm, and aligns the supporting plate by the alignment signal receiver according to the position rectification signal.